1. Field of the Invention
The present invention relates to a method of forming electrical connection and in particular to a method of forming an electrical connection with improved integrity and stability over a wide temperature range.
2. Description of the Prior Art
Various methods of forming electrical connections are known such as soldering, welding or the use of electrically conductive epoxy adhesives.
There are, however, problems in forming a suitable high integrity electrical connection between terminals and a terminal pad which is deposited on a substrate such as metal, steel or ceramic or a substrate comprising one or more metal, steel or ceramic components or layers. Most conventional methods and materials used for attaching terminals have an upper temperature limit beyond which the original characteristics no longer hold so that electrical connections so formed are incapable of maintaining their attachment integrity over a wide temperature range.
All known prior art methods of attaching terminals to terminal pads printed on substrates give electrical connections with limited integrity specifically as it approaches its upper operating temperature.
Such known methods include:
i) solder which is effective up to 200.degree. C. and in any case is time consuming PA1 ii) the use of silver loaded epoxy is effective up to 250.degree. C. but is expensive and time consuming PA1 iii) the use of glass loaded epoxy which extends the temperature range up to 400.degree. C. but is very expensive and time consuming PA1 iv) spring loaded contacts which are at best useful up to 300.degree. C. are very complicated, time consuming and have a limited operating life; in addition the integrity reduces with age PA1 v) conventional methods of welding such as an electric arc or flame-burner welding, but these are not technically appropriate for terminal pads on a ceramic or ceramic based or coated substrate.
The present invention has been made from a consideration of these problem.